190-01639-00
GSU 75 ADAHRS Installation Manual
Rev. 6
Page 2-8
2.11.2 GMU 44 Magnetometer Mounting
The GMU 44 is an extremely sensitive three-axis magnetic sensor. It is more sensitive to nearby magnetic
disturbances than a flux gate magnetometer. For this reason, when choosing a mounting location for the
GMU 44, observe the following distances from objects or devices that can disturb the magnetic field.
Table 2-8 specifies recommended distances from magnetic disturbances for GMU 44 location.
Ensure that any electrical conductor that comes within 10 feet (3.0 meters) of the GMU 44 is installed as a
twisted shielded pair, not a single-wire conductor. (If possible, the shield should be grounded at both ends.)
Use nonmagnetic materials to mount the GMU 44, and replace any magnetic fasteners within 0.5 meter
with nonmagnetic equivalents (e.g. replace zinc-plated steel screws used to mount wing covers or wingtips
with nonmagnetic stainless steel screws.).
In general, wing or tail mounting of the GMU 44 magnetometer is strongly preferred. Fuselage mounting is
strongly discouraged because of numerous potential disturbances that interfere with accurate operation.
For installations with dual GMU 44 magnetometers, co-locating the two magnetometers close to each
other in the tail or one wing is recommended because this reduces the likelihood of heading splits or
miscompares when operating on the ground in the vicinity of local magnetic anomalies.
Mechanical mounting fixtures for the GMU 44 must be rigidly connected to the aircraft structure. Use of
typical aircraft-grade materials and methods for rigid mounting of components is acceptable, so long as
adequate measures are taken to ensure a stiffened mounting structure.
Align the GMU 44 mounting rack to within 3.0° of the aircraft level reference in pitch and roll.
The GMU 44 must be mounted with its mounting rack’s forward direction aligned in heading to within
2.5° with the forward longitudinal direction of the aircraft. Furthermore, alignment to within 0.5° with the
forward longitudinal direction of the aircraft is strongly preferred. If alignment in heading to within 0.5° is
not possible, it is strongly recommended to complete the post-installation heading offset procedure which
is described in
.
It is strongly preferred that the GMU 44 alignment is within 0.5° of the aircraft forward longitudinal
directional, rather than using the heading offset procedure.
Table 2-8 Recommended Distance from Magnetic Disturbances
Disturbance Source
Minimum Distance from GMU 44
Electric motors and relays, including servo motors
10 feet (3.0 meters)
Ferromagnetic structure greater than 1 kg total (iron, steel, or
cobalt materials, especially landing gear structure)
8.2 feet (2.5 meters)
Ferromagnetic materials less than 1 kg total, such as control
cables
3 feet (1.0 meter)
Any electrical device drawing more than 100 mA current
3 feet (1.0 meter)
Electrical conductors passing more than 100 mA current [(must
be twisted shielded pair if within 10 feet (3.0 meters)]
3 feet (1.0 meter)
Electrical devices drawing less than 100 mA current
2 feet (0.6 meter)
Magnetic measuring device other than another GMU 44 (e.g.
installed flux gates, even if not powered)
2 feet (0.6 meter)
Electrical conductors passing less than 100 mA current [(must
be twisted shielded pair if within 10 feet (3.0 meters)]
1.3 feet (0.4 meter)
340095
The document reference is online, please check the correspondence between the online documentation and the printed version.
